The present invention relates to a method and apparatus for laying a filament, and in particular, but not exclusively, to a method and apparatus for laying a weft yarn onto a substrate on which the weft yarn is to be secured.
One application where it is necessary to lay a weft yarn onto a substrate occurs in the manufacture of reinforced plastics sheeting, the plastics sheeting being reinforced with a first set of fibres arranged perpendicularly to a second set of fibres.
The known method for producing such a reinforced sheet is to first apply the plastics to a paper backing sheet withdrawn from a storage roll, the plastics being applied in liquid form, usually in the form of a solution. Reinforcing weft fibres are then laid across the width of the backing paper onto the liquid plastics, and are embedded therein. This is conventionally done by means of a travelling head which traverses across the width of the backing sheet and which lays down a weft yarn which sinks into, and becomes embedded in, the liquid plastics. By traversing backwards and forwards, a series of weft yarns is produced. However, in order to position the yarns perpendicularly to the direction of motion of the travel of the backing sheet, it is necessary for the travelling head to traverse at a precisely calculated angle to the direction of motion of the paper, otherwise the threads will not be perpendicular to the length of the finished product. Also, this process is necessarily slow since in order to obtain reasonable accuracy the travelling head must not travel too quickly. It is possible to speed up the process by having a plurality of travelling heads, each dispensing its own weft yarn, but the cost of such apparatus is significantly increased. Moreover, the problem with all such travelling heads is that the resultant yarn laid down onto the plastics is not particularly accurate, in that the spacings between adjacent weft yarns can vary by several millimeters, perhaps as much as 5 mm in either direction from the correct location. This does not cause too much of a problem when the spacing of adjacent weft yarns is intended to be relatively large, but if the spacing of adjacent weft yarns becomes smaller, then the error involved in using the above apparatus becomes significant.
Once the weft yarns are laid onto the plastics, a series of parallel, equally- spaced warp yarns extending parallel to the direction of motion of the backing paper, are laid down on top of the weft yarns and onto the plastics, in which they become embedded. The construction is subsequently passed through various further treatments and drying stages to produce the finished product.
As stated above, in order to achieve reasonable speed, it is necessary to have a plurality of dispensing heads, and even so the accuracy obtained with the prior art devices is not good.